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//===- MemoryDependenceAnalysis.cpp - Mem Deps Implementation --*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the Owen Anderson and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements an analysis that determines, for a given memory
// operation, what preceding memory operations it depends on. It builds on
// alias analysis information, and tries to provide a lazy, caching interface to
// a common kind of alias information query.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Instructions.h"
#include "llvm/Function.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Target/TargetData.h"
using namespace llvm;
char MemoryDependenceAnalysis::ID = 0;
Instruction* MemoryDependenceAnalysis::NonLocal = (Instruction*)0;
Instruction* MemoryDependenceAnalysis::None = (Instruction*)~0;
// Register this pass...
RegisterPass<MemoryDependenceAnalysis> X("memdep",
"Memory Dependence Analysis");
/// getAnalysisUsage - Does not modify anything. It uses Alias Analysis.
///
void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequiredTransitive<AliasAnalysis>();
AU.addRequiredTransitive<TargetData>();
}
/// getDependency - Return the instruction on which a memory operation
/// depends. NOTE: A return value of NULL indicates that no dependency
/// was found in the parent block.
Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
bool local) {
if (!local)
assert(0 && "Non-local memory dependence is not yet supported.");
// Start looking for dependencies with the queried inst
BasicBlock::iterator QI = query;
// Check for a cached result
std::pair<Instruction*, bool> cachedResult = depGraphLocal[query];
// If we have a _confirmed_ cached entry, return it
if (cachedResult.second)
return cachedResult.first;
else if (cachedResult.first != NonLocal)
// If we have an unconfirmed cached entry, we can start our search from there
QI = cachedResult.first;
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
BasicBlock::iterator blockBegin = query->getParent()->begin();
// Get the pointer value for which dependence will be determined
Value* dependee = 0;
if (StoreInst* S = dyn_cast<StoreInst>(QI))
dependee = S->getPointerOperand();
else if (LoadInst* L = dyn_cast<LoadInst>(QI))
dependee = L->getPointerOperand();
else if (FreeInst* F = dyn_cast<FreeInst>(QI))
dependee = F->getPointerOperand();
else if (isa<AllocationInst>(query)) {
// Allocations don't depend on anything
depGraphLocal.insert(std::make_pair(query, std::make_pair(None,
true)));
reverseDep.insert(std::make_pair(None, query));
return None;
} else {
// Non-memory operations depend on their immediate predecessor
--QI;
depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
reverseDep.insert(std::make_pair(QI, query));
return QI;
}
// Start with the predecessor of the queried inst
--QI;
TargetData& TD = getAnalysis<TargetData>();
while (QI != blockBegin) {
// If this inst is a memory op, get the pointer it accessed
Value* pointer = 0;
if (StoreInst* S = dyn_cast<StoreInst>(QI))
pointer = S->getPointerOperand();
else if (LoadInst* L = dyn_cast<LoadInst>(QI))
pointer = L->getPointerOperand();
else if (isa<AllocationInst>(QI))
pointer = QI;
else if (FreeInst* F = dyn_cast<FreeInst>(QI))
pointer = F->getPointerOperand();
else if (CallInst* C = dyn_cast<CallInst>(QI)) {
// Call insts need special handling. Check is they can modify our pointer
if (AA.getModRefInfo(C, dependee, TD.getTypeSize(dependee->getType())) !=
AliasAnalysis::NoModRef) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(C, true)));
reverseDep.insert(std::make_pair(C, query));
return C;
} else {
continue;
}
}
// If we found a pointer, check if it could be the same as our pointer
if (pointer) {
AliasAnalysis::AliasResult R = AA.alias(
pointer, TD.getTypeSize(pointer->getType()),
dependee, TD.getTypeSize(dependee->getType()));
if (R != AliasAnalysis::NoAlias) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
reverseDep.insert(std::make_pair(QI, query));
return QI;
}
}
QI--;
}
// If we found nothing, return the non-local flag
depGraphLocal.insert(std::make_pair(query,
std::make_pair(NonLocal, true)));
reverseDep.insert(std::make_pair(NonLocal, query));
return NonLocal;
}
/// removeInstruction - Remove an instruction from the dependence analysis,
/// updating the dependence of instructions that previously depended on it.
void MemoryDependenceAnalysis::removeInstruction(Instruction* rem) {
// Figure out the new dep for things that currently depend on rem
Instruction* newDep = NonLocal;
if (depGraphLocal[rem].first != NonLocal) {
// If we have dep info for rem, set them to it
BasicBlock::iterator RI = depGraphLocal[rem].first;
RI++;
newDep = RI;
} else if (depGraphLocal[rem].first == NonLocal &&
depGraphLocal[rem].second ) {
// If we have a confirmed non-local flag, use it
newDep = NonLocal;
} else {
// Otherwise, use the immediate successor of rem
// NOTE: This is because, when getDependence is called, it will first check
// the immediate predecessor of what is in the cache.
BasicBlock::iterator RI = rem;
RI++;
newDep = RI;
}
std::multimap<Instruction*, Instruction*>::iterator I = reverseDep.find(rem);
while (I->first == rem) {
// Insert the new dependencies
// Mark it as unconfirmed as long as it is not the non-local flag
depGraphLocal[I->second] = std::make_pair(newDep, !newDep);
reverseDep.erase(I);
I = reverseDep.find(rem);
}
}
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